Is it possible to change the pem file after creating an Instance

Question

I actually have lost the key file for accessing my EC2 instance can anyone help me as how to get it or change the key file?

Answer 1

You can refer this documentation from amazon:-

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-key-pairs.html#replacing-lost-key-pair

Answer 2

Here are the steps you can follow:- I got it from a blog i read few days back. 

1. Stop the running EC2 instance
2. Detach its /dev/xvda1 volume (let's call it volume A) 
3. Start new t1.micro EC2 instance, using my new key pair. Make sure you create it in the same subnet, otherwise you will have to terminate the instance and create it again.
4. Attach volume A to the new micro instance, as /dev/xvdf (or /dev/sdf)
5. SSH to the new micro instance and mount volume A to /mnt/tmp
6. $ sudo mount /dev/xvdf1 /mnt/tmp
7. Copy ~/.ssh/authorized_keys to /mnt/tmp/home/ubuntu/.ssh/authorized_keys
8. Logout
9. Terminate micro instance
10. Detach volume A from it
11. Attach volume A back to the main instance as /dev/xvda
12. Start the main instance
13. Login as before, using your new .pem file